Why would your doctor change a medicine?

I had a bad attack in the beginning of August so I've been on dulera for the past 2 months and told to not take pulmicort. Now today my doctor recommended I go back to my pulmicort. What would the reason be for this as it seems the dulera works just as well as the pulmicort did before my attack? I did message my doctor and ask him as he recommended it through the patient portal I still have an appointment to see him at the end of October. I like to get your folks opinion as well 😀